In the brazing of an aluminum material one uses a brazing alloy which has a melting point that is somewhat lower than that of the aluminum material being brazed. A typical brazing alloy is a eutectic alloy of aluminum and silicon. The flux rids the aluminum material and brazing alloy of braze-inhibiting substances such as oxide films.
A popular flux today is composed of a KF-AlF.sub.3 complex or complexes; it melts at 560.degree. C. or above. Brazing under a blanket of inert gas, e.g., nitrogen, is usual with this flux. For lower-melting fluxes lithium and cesium have been reacted-in (complexed) as fluoaluminates and applied to the workpieces in various ways, e.g., in particulate or aqueous form.
In the past, some frequently-used flux materials for brazing aluminum were mixtures of chlorides such as zinc chloride and sodium chloride with fluorides. The current brazing practice seems to have turned its back on the use of chlorides, presumptively because they got the reputation of sometimes corroding the aluminum material. Additionally, collateral brazing technology (not the brazing of aluminum material) utilizing cesium and rubidium fluorides teaches expressly to avoid the use of the corresponding chlorides of these metals because they tended to form slags and other residues which are detrimental to the brazing.
Now I have found ways to use these two chlorides, CsCl and RbCl, in the brazing of an aluminum material quite successfully--surprisingly without the aforementioned detractions from performance; and, furthermore, with an ability to braze (in many cases without the use of an inert gas blanket) a wider than previous range aluminum material compositions; and also to use a wider than previous range of brazing alloys (often called "filler metal"). Some of this stems from surprisingly low flux melting points attainable.